Conventionally, in order to improve heat insulating properties and heat shielding properties of an aluminum-based member used in a vehicle and the like, an anodic oxide film having a pore inside has been formed on a surface of the aluminum-based member.
For example, Japanese Patent Application Laid-Open No. 2015-31226 describes a constitution including an anodic oxide film with low heat conduction and a low volume specific heat capacity on a part of or the whole of a wall surface facing a combustion chamber of an internal combustion engine. According to this Japanese Patent Application Laid-Open No. 2015-31226, this anodic oxide film has its film thickness within a range of 30 to 170 μm and has a first micro pore having a micro-sized diameter and extending from a surface of the anodic oxide film toward an inside in a thickness direction or in a substantially thickness direction, a nano pore having a nano-sized diameter, and a second micro pore located inside the anodic oxide film and having a micro-sized diameter. Moreover, it has a structure in which at least a part of the first micro pore and the nano pore is sealed by a sealing agent, but at least a part of the second micro pore is not sealed.
Moreover, according to Japanese Patent Application Laid-Open No. 2015-31226, an aluminum-based material forming an aluminum-based wall surface contains at least one kind of Si, Cu, Mg, Ni, and Fe as an alloy component.
By having the alloy component contained or particularly by having at least one kind of Si, Cu, Mg, Ni, and Fe contained as the alloy component in the aluminum-based material, it is described that the diameter or a sectional dimension of the micro pore tends to further increase, expansion of a diameter of the micro pore is promoted, and porosity can be improved.